Pressures  of  Alcoholic  Solutions, 
601 
cell.  By  keeping  the  chest  packed  with  broken  ice,  the 
temperature  inside  remained  steady  at  zero.  The  temperature 
near  the  gauge  at  the  outer  surface  was  very  steady  at  about 
11°'5  C.  There  was  a  very  small  volume  of  solution  above 
the  mercury  in  the  gauge  which  was  above  the  inside 
temperature. 
The  conductivity  of  the  solutions  was  found  after  the  steady 
value  for  the  pressure  was  obtained.  The  liquid  was  with- 
drawn from  the  cell  and  5'4  c.c.  (giving  what  seemed  to  be  a 
suitable  depth  of  liquid)  were  used  in  a  small  electrolytic  cell. 
The  electrodes  were  small  platinum  plates,  platinized  and 
then  heated  to  redness.  The  commutator  and  galvanometer 
method  of  Fitzpatrick  and  Whetham  was  used  in  finding  the 
electrolytic  resistance.  The  cell  was  standing  in  broken  ice 
for  at  least  an  hour  before  readings  were  taken.  The  resistance 
of  the  cell  was  found  ;  the  battery  reversed  and  the  resistance 
again  found.  The  electrolytic  cell  was  then  reversed  and 
two  observations  of  its  resistance  taken  as  before.  The 
inverse  of  the  mean  of  these  four  values  was  taken  as  the 
conductivity,  thus  eliminating  as  far  as  possible  polarization 
effects  in  the  cell,  and  thermoelectric  effects  in  the  commu- 
tator. The  following  table  contains  all  the  readings  I  have  been 
4ible  to  get  during  five  weeks  by  means  of  cell  B  in. : — 
Strength 
of 
Solution. 
Theoretical 
Pressure 
(van't  Hoff) 
at  0°  C. 
Observed  Pressure 
at  0°  C. 
Conductivity  (=~  j 
at  0°  C. 
•144  normal. 
•089 
•040 
■020 
2440  mm. 
1660 
690 
345 
195  mm. 
208 
131 
76 
•0042 
•0029 
•0016 
•00087 
The  last  experiment  was  made  using  the  ordinary  absolute 
alcohol;  these  values  therefore  may  not  altogether  agree 
with  previous  values,  but  it  does  not  seem  likely  that  the  use 
of  this  alcohol  will  have  greatly  affected  the  readings. 
The  following  curves  (pp.  602-3)  are  obtained  from  the 
numbers  in  the  above  table. 
The  differences  in  Curves  II.  and  III.  are  such  as  are 
accounted  for  by  the  form  of  Curve  IV.  The  conductivity 
falls  off  rather  more  quickly  than  the  strength. 
Phil.  Mag.  S.  6.  Vol.  11.  No.  61.  April  1906.         '2  R 
